FIX: Locale mismatch at theme translations picker (#26687)

* FIX: Locale mismatch at theme translations picker

Before, the theme translations picker value was set to the
site's default locale, which mismatches from the user's locale.

This commit changes the picker value to the user locale.

relates to https://meta.discourse.org/t/locale-mismatch-at-theme-translations/302879

* DEV: Address code review feedback.

- https://github.com/discourse/discourse/pull/26687#discussion_r1572516758
- https://github.com/discourse/discourse/pull/26687#discussion_r1572524059

app/assets/javascripts/admin/addon/controllers/admin-customize-themes-show.js

@@ -302,7 +302,11 @@ export default class AdminCustomizeThemesShowController extends Controller {
   }
 
   get locale() {
-    return this.get("model.locale") || this.siteSettings.default_locale;
+    return (
+      this.get("model.locale") ||
+      this.userLocale ||
+      this.siteSettings.default_locale
+    );
   }
 
   @action

app/assets/javascripts/admin/addon/routes/admin-customize-themes-show.js

@@ -41,6 +41,7 @@ export default class AdminCustomizeThemesShowRoute extends Route {
       colorSchemes: parentController.get("model.extras.color_schemes"),
       editingName: false,
       editingThemeSetting: false,
+      userLocale: parentController.get("model.extras.locale"),
     });
 
     this.handleHighlight(model);

app/controllers/admin/themes_controller.rb

@@ -176,6 +176,7 @@ class Admin::ThemesController < Admin::AdminController
       themes: serialize_data(@themes, ThemeSerializer),
       extras: {
         color_schemes: serialize_data(@color_schemes, ColorSchemeSerializer),
+        locale: current_user.effective_locale,
       },
     }
 

spec/system/admin_customize_themes_spec.rb

@@ -3,7 +3,7 @@
 describe "Admin Customize Themes", type: :system do
   fab!(:color_scheme)
   fab!(:theme)
-  fab!(:admin)
+  fab!(:admin) { Fabricate(:admin, locale: "en") }
 
   let(:admin_customize_themes_page) { PageObjects::Pages::AdminCustomizeThemes.new }
 
@@ -160,5 +160,33 @@ describe "Admin Customize Themes", type: :system do
       theme_translations_settings_editor.fill_in("Hello World in French")
       theme_translations_settings_editor.save
     end
+
+    it "should match the current user locale translation" do
+      SiteSetting.allow_user_locale = true
+      SiteSetting.set_locale_from_accept_language_header = true
+      SiteSetting.default_locale = "fr"
+
+      theme.set_field(
+        target: :translations,
+        name: "en",
+        value: { en: { group: { hello: "Hello there!" } } }.deep_stringify_keys.to_yaml,
+      )
+      theme.set_field(
+        target: :translations,
+        name: "fr",
+        value: { fr: { group: { hello: "Bonjour!" } } }.deep_stringify_keys.to_yaml,
+      )
+      theme.save!
+
+      visit("/admin/customize/themes/#{theme.id}")
+
+      theme_translations_settings_editor =
+        PageObjects::Components::AdminThemeTranslationsSettingsEditor.new
+
+      expect(theme_translations_settings_editor.get_input_value).to have_content("Hello there!")
+
+      theme_translations_picker = PageObjects::Components::SelectKit.new(".translation-selector")
+      expect(theme_translations_picker.component.text).to eq("English (US)")
+    end
   end
 end